96 Mr. Rennet's Experiments on a new 
applied ; but without producing any sensible effect on the 
needle. 
In the LXXVIth Volume of the Philosophical Transac- 
tions, Mr. Cavallo has endeavoured to prove, that brass 
“ does not owe its magnetism to iron, but to some particular 
“ configuration of its component particles, occasioned by the 
“ usual method of hardening it, which is by hammering." 
Some brass, he observes, will not acquire “ any sensible mag- 
“ netism by hammering." And in other ' pieces, which have 
often passed from the workshop to the furnace, and from the 
latter to the former, there is contained iron, which renders 
them magnetic. 
Now, since some brass is evidently magnetic because it 
contains iron, it appears to me likely that brass, whose mag- 
netism is made sensible by hammering, contains a smaller 
quantity of iron, and that hammering renders it sensible, by 
giving it some degree of polarity. Therefore no brass can 
acquire this property which contains no iron. This will 
appear more evident by the following experiments. 
EXPERIMENT XVII. 
I placed an iron nail, about two inches long, in the fire, 
where it became red hot, and cooled, as the fire went out, in 
a position east and west with respect to the magnetic meri- 
dian ; by which it became very soft, and when presented to- 
wards the needle, it attracted or repelled according to its po- 
sition, having no fixed polarity. The nail was then placed 
upon an anvil, with the point directed towards the south of 
the magnetic meridian ; and after hammering in this position 
till it was considerably hardened, its point possessed a fixed 
